The present invention relates to a novel apparatus and process for measuring with great accuracy and great rapidity the colloidal stability of liquids, and particularly nutritious liquids of the beer,wine,oil type.
Measuremenat of the turbidity of nutritious liquids, when cold, is of great importance in that it has enabled, and still enables at the present time, the improvement of the colloidal stability of beers, wines and other drinks obtained by fermentation, or gaseous drinks, as well as the limpidity of oils when cold.
In particular insofar as the measurement of the turbidity of cold beers is concerned, the first tests proposed measured the tendency to the formation of turbidity in beers while maintaining the beers being tested for 7 days at a temperature of 40.degree. C., then for 24 hours at a temperature of 0.degree. C. (EBC test) Extracted from the statistical study of the results thus obtained was a correlation between the values found by the EBC tests and the sparkle of the beer after 6 months storage at ambient temperature, with a highly significant coefficient.
The EBC tests, lasting 8 days, presented however the major disadvantage of their length and very often they could only be carried out after the beer had left the brewery when no correction could obviously be made to the treatment of the beer. An important improvement was made to the measurement of the turbidity of cold beers, by L. CHAPON and M. CHEMARDIN (see EBC Proceeding 1967, Madrid, p. 389-405) by means of the "alcohol-cold" test which enables the development of the turbidity of the beer at -8.degree. C. for 40 minutes, by adding thereto from 0 to 6% of ethanol. The principle of this test makes use of the ethanol enrichment of the beer to cause therein the formation of turbidity when cold. Through its hydroxyl group, ethanol may play the role of proton donor and is associated, by hydrogen bonds, with the peptidic groups of the protein part of the protein-tannin associations which form the particles of the turbidity when cold, driving out their solvation water molecules, and thus reducing their solubility. This reduction of solubility is all the more marked the lower with temperatures of beer. The apparatus for the cold measurement of turbidity perfected by L. CHAPON and M. CHEMARDIN (see above quotation) comprised a nephelometer refrigerated by means of a Peltier element to a constant temperature between -8.degree. and +20.degree. C., a light source formed by a 30 W lamp supplied with a voltage of 6 V, cells for measuring the diffused light formed by barrier-layer cells, a current detector formed by a galvanometer, a recorder formed by a Sefram spot-follower and a potentiometric recorder for recording turbidity curves as a function of the temperature. Calibration of the nephelometer was achieved by means of formazine solutions. This apparatus has been perfected by the Applicant (see French Patent TEPRAL No. 73 09798 of Mar. 12, 1973).
A large number of apparatuses, like the CHAPON and CHEMARDIN apparatus, which rely on the measurement of light diffused at different angles, have been proposed in the prior art. They do not allow however absolute determination of the turbidity, for they cannot take into account the microscopic nature of the turbidity of beer, which is formed by particles of varying size, and which has been established by electronic microscopy as being between 0.1 and 1 micron so that the precise determination of the turbidity of beer requires measuring methods and apparatuses which take into account the size of the particles. From this new point of view, KLINE and AXILROD have proposed an apparatus for the photoelectric determination of turbidity, formed by a photoelectric colorimeter in which two transmission readings are carried out (at 440 nm in a tank of 5 cm diameter or at 580 nm in a tank of 20 mm diameter), at about 10 cm from the photoelectric cell. The readings are then converted into optical densities and the difference between these values depend on the total light diffused and represent the measurement of the turbidity. CLEASSON and SANDEGREN have also proposed associating, for the measurement of cold turbidity, the dispersion of the light and electronic microscopy. The same Authors have developed an apparatus for measuring the size of the particles by Doppler effect, by measuring the difference between the emission wavelength of a laser on a turbidity sample and that of the diffused light, to deduce therefrom the speed of the particles, then their size.
Furthermore, there has been proposed (see J. E. CAUPEIL, Unilever Research, "Revue Francaise des Corps Gras", No. 8-9 August-September 1977, p. 427-431) an apparatus for the rapid measurement of the limpidity of oils, by laser. This apparatus comprises,: a pump which causes the oil sample to be checked to flow through a spiral bathed in an oil bath brought up to 100.degree. C., then through a first measuring cell, then through a spiral placed in melting ice, then finally through a second measuring cell; two laser light sources; two microscopes placed in front, which serve for visual observation; two microscopes placed in the rear, which serve to form an enlarged image of the laser ray on a diaphragm placed in front of the corresponding detector; and two detectors each formed by an electron photomultiplying tube (EPT) which transforms the light signal into an electric current, which is transformed into a potential difference by a potentiometric recorder. The number of mV read after the first measurement, made after heating to 100.degree. C., is subtracted from the number of mV read after the second measurement, made after cooling to 0.degree. C. The difference obtained from the two readings made on the recorder is the measurement of the quantity of crystals present in the oil, whose concentration is read from a standard curve. The measurement operation is carried out within 15 minutes, whereas the cold tests previously used lasted several days.